Re: [PATCH 1/5] common: don't (kind of) open-code rcu_lock_domain_by_any_id()

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 05/01/2021 13:24, Jan Beulich wrote:
> Even more so when using rcu_lock_domain_by_id() in place of the more
> efficient rcu_lock_current_domain().
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

> ---
> Besides get_pg_owner(), gnttab_copy_lock_domain() has similar strange(?)
> behavior: They accept DOMID_SELF, but not the resolved ID of the caller.

I queried that behaviour years and years ago.

According to Keir, it is part of the attempt to force guests to not know
their own domid.  Xen itself does (or did) its very hardest to prevent a
domU knowing its own domid, while at the same time the "domid" key in
xenstore is mandatory for setting up PV rings.

I'd personally think was a short sighted move.

~Andrew